The present invention relates to a method for influencing the electrical power of a load with the assistance of a pulse-width modulated signal. From the textbook by L. Retzbach, xe2x80x9cSpeed Controllers,xe2x80x9d Neckar Printing House, Villingen-Schwenningen, 2nd edition, 1982, a method is described for influencing the electrical power of DC-current electromotors with the assistance of a pulse-width modulated signal. On pages 21-24, a principle of speed regulation is described that includes a pulse-width modulator. A comparator designated as modulator compares a DC voltage, which is a measure for the setpoint value of the electrical power of the DC-electromotor, with an AC voltage, which supplies a sawtooth voltage generator. The time during which the DC voltage exceeds the AC voltage signal, determines, for example, the turn-on time. The duration of the fundamental period of the generated pulse-width modulated signal is set by the fundamental frequency of the sawtooth voltage generator. In the generation of the pulse-width modulated signal, two limiting cases can arise that are not described in greater detail in the cited literature. The limiting cases arise when the DC voltage consistently lies beneath or above the sawtooth-shaped voltage made available by the generator. In one operational case, no further turn-on times occur. The electromotor is then no longer supplied with current. In the other operational case, the pulse-width modulated signal changes into a continuous turn-on signal, so that the electromotor continually is fully supplied with current.
Protection of the electromotor against overloading and of the output-stage circuit against the occurrence of an overcurrent is provided by the motor current detector described on pages 83 and 84. One implementation provides for the evaluation of the voltage drop occurring on the contact-break distance of the output-stage switch during the turn-on time.
The present invention is based on the objective of indicating a method for influencing the electrical power of a load with the assistance of a pulse-width modulated signal, the latter including the requirement of a continuous turn-on signal, which makes possible the detection of an operational quantity of the load.
The method according to the present invention has the advantage that in stipulating a continuous turn-on signal, which can arise as a limiting case in response to a pulse-width modulated signal, an operational quantity of the load can be detected that can only be detected through an at least short-duration change in the electrical power supplied to the load. An operational quantity of this type is, for example, a current change that arises in response to a change in the electrical power fed to the load.
In this regard, the present invention provides that the continuous turn-on signal is terminated using an interrupt signal and that the continuous turn-on signal is followed by a clock-pulse phase having at least a fundamental period duration of the pulse-width modulated signal, the period including a turn-off time.
The method according to the present invention has the advantage that, on the one hand, the load, in the context of the influencing of the electrical power with the assistance of a pulse-width modulated signal, can be provided with at least approximately full power and, on the other hand, a change in the electrical power of at least short duration arises, the short-duration change being able to be used, for example, for detecting an operational quantity of the load.
A particularly advantageous embodiment of the method according to the present invention provides that a program-controlled signal-processing arrangement, which preferably generates the pulse-width modulated signal, generates the interrupt signal after one program cycle. Using this measure, a simple realization of the program flow sequence is achieved. In particular, the advantage arises that the program running in the signal-processing arrangement brings to bear an influence on the electrical power of the load, upon the generation of the interrupt signal, at exactly the moment at which the program of the signal-processing arrangement expects the effects of the power change. In this manner, an unnecessary halt in the ongoing program flow is avoided.
Another advantageous embodiment provides that the interrupt signal arises due to an external request signal. On the basis of this measure, a controlled termination of a continuous turn-on signal is possible, the external request signal being preferably generated by the arrangement which detects the operational quantity of the load.
Further advantageous embodiments provide that the duration of the clock-pulse phase, which follows the continuous turn-on signal, amounts to a whole-number multiple of the fundamental period duration of the pulse-width modulated signal.
The method according to the present invention makes possible the detecting of a measuring quantity in the area of the turn-off time, which arises during the clock-pulse phase. A measuring quantity of this type is, for example, a change in the current flowing through the load. The current change, at an inductive component located in the circuit, for example, at an inductance-susceptible printed circuit trace of a printed circuit, leads to an inductive voltage drop which is proportional to the current change. Using an integrator, the absolute current can be inferred from the current change.